
of migration to settle down directly onto the area, while relatively few other 
birds passed through it. 
Nesting population 
A few early mallards and pintails arrived on the Waubay area in late 
March or early April when the first open water appeared. They usually pre- 
ceded the main flight by 2 or 3 weeks. Figure 11 shows the movement of 
"indicated breeding pairs" (pairs, lone males, and lone females) onto the 
area in the spring of 1951 when the area was censused most frequently. Main 
breeding populations of blue-winged teal and gadwall arrived considerably later 
than the first arrivals, while mallards and pintails, with the exception of a 
few very early pioneers, arrived more or less in a body. The pattern of 
arrival was much the same in the other three years. 
The size and species composition of the breeding population are shown in 
table 5. The first four columns, under "Peak date,” represent the time the 
greatest breeding population of each species was measured. However, since the 
peak date represents the center of a plateau when the population was relatively 
stable (fig. 11), these dates are of only limited value for comparing years. 
The next four columns show the population of each species, in terms of indica- 
ted pairs per square mile, when each was at its height during each of the four 
years. In no year did all species reach their peaks-on the same date. How- 
ever, the total is a measure of the entire breeding potential of the spring 
population. The trend in breeding populations of most species was upward 
through 1952. The 1953 population decreased from that of 1951 and 1952, but 
still was higher than in 1950. The last two columns show the average popu- 
lations and the species composition for the 4 years. The blue-winged teal was 
by far the most abundant duck while the four most important species made up 
almost 86 percent of the breeding population. 
When each species was at its peak nesting population, few individuals 
were tallied as nonbreeders. Table 6, showing the blue-winged teal population 
in 1951, indicates the relation between breeders and nonbreeders. 
At the time most of the breeding blue-winged teal had arrived (May 4 to 
May 22), few were nesting and most were seen as pairs, with a few migrants 
and courting parties still in evidence. Two to three weeks later (May 23 to 
June 3), nesting was well underway, and more than half of the pairs were 
represented by lone males, grouped males still being scarce. About 3 weeks 
later (June 14 to July 9), there was an increase in grouped males that had 
deserted their hens, then in the last stages of incubation. In the case of 
‘the blue-winged teal, where the drakes stayed with their hens until nearly 
hatching time, this increase in grouped males coincided with the appearance of 
broods. In other species, such as the mallard and pintail, whose drakes de- 
serted their hens soon after incubation started, grouped drakes were conspicuous 
before broods appeared. By mid-July, when the young of the year were beginning 
to fly and field classification of the birds was no longer feasible, they were 
classed as "flying". By mid-August, populations were greatly increased by 
early migrants from other areas. 
There were few complicating factors as long as the population of each 
species was computed when at its peak. Only 10 grouped blue-winged teal 
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